Abstract

Abstract

Since pigeon pea [Cajanus cajan L. (Millsp.)] has a considerable potential as a tropical legume, intensive research in the Caribbean is being undertaken with a view to increase production. There is a scarcity of information on the effectiveness of Rhizobium of the pigeon pea to fix atmospheric N and to meet the N needs of the crop. Moreover, conflicting results have been reported on the effect of fertilizer N on grain yield, presumably because of variable mineral N levels in soil. Therefore the present investigation was designed to study the effect of changes in soil mineral N levels (brought about initially by incorporation of coconut fibre and bagasse with soil at the rate of 25 metric tons/ha each) and five Rhizobium strains (two local, UWI 10004 and UWI 10013, and three exotic, iCPE(a), CB756 and CIAM/1001) on nodulation, nitrogenase activity and grain yield of the crop. Greenhouse and field experiments were conducted on a River Estate Loam, a fluventic eutropept, at the University Field Station, Trinidad. The results showed that the incorporation of coconut fibre and begasse reduced soil mineral N levels through immobilization and led to early nodule formation and nitrogenase activity. Although the incorporation of coconut fibre increased plant shoot weight after 14 weeks growth, that of bagasse immobilized so much mineral N (from initial level of 50 ppm N to 6 ppm N at 7 wcxks after application) that plants were N starved. The dry pod yield was increased by all Rhizobium strains. However the grain yield was significantly increased by the exotic strains, iCPE(a) and CIAM/1001. Thus, by manipulating soil mineral N levels and by using effective Rhizobium strains, the pigeon pea grain yields can be increased.

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